This invention relates to an improved process for the production of low shrinkage polyester fibers which are particularly useful in the preparation of reinforced elastomeric structures. More particularly, it relates to a continuous process for the production of low shrinkage polyester fibers by melt-spinning the polymer followed immediately by drawing and heat treating the spun fibers.
The production of polyester filaments useful for textile and industrial purposes is known. In many of the prior art methods, the spinning and drawing of the filaments are separately carried out. However, several processes have been developed which involve conditions of continuously spinning and drawing filaments.
U.S. Pat. No. 3,413,797 to Roy Chapman discloses that drawn polyester yarns having reduced shrinkage can be produced by heat treating the drawn yarns by passing them through a fluidized bed of solid particles maintained at a temperature of 240.degree.-264.degree. C.
More recently, it has been suggested in U.S. application Ser. No. 278,922, filed Aug. 9, 1972, now abandoned that low shrinkage polyester yarns can be produced by melt-spinning of a polyester polymer by substantially simultaneous spinning, lubricating, drawing and heat treating the fibers under controlled conditions. However, in commercial operation of this process at high throughput rates of 50 pounds per hour or greater through the spinneret, serious problems have been encountered in that uniform low shrinkage yarn could not be produced. In addition, problems have been encountered due to "flicking" of filaments from the main yarn bundle above the lube roll, which flicking results in production of yarn of relatively poor quality. Accordingly, research has been continued to solve these deficiencies.
The term "RMS," which is short for root-mean-square, is an arbitrary measurement of surface texture and is described in detail in the publication, Surface Texture (ASA B 46.1 - 1962), the American Society of Mechanical Engineers, United Engineering Center, 345 East 47th Street, N.Y. 17, New York, page 16 (1962). Such measurement is utilized throughout this invention disclosure unless otherwise stated.
The term "flicking" is conventionally applied and is used herein to mean a momentary slackness of a filament in the undrawn yarn above the lube roll. The slack filament bows out of phase from the main bundle, thus "flicking." It is known that excessive "flicking" normally causes production of yarn of relatively low quality having an excessive number of defects such as missing filaments, filament breaks and loops.